Variable width constant current driver



Feb. 16, 1960 v E. F. MYERS ETAL 2,925,492

' VARIABLE WIDTHCONSTANT CURRENT DRIVER Filed Aug. 31.- 1956' t (MICROSECONDS) 1 (0 GRID BIAS) m@ INVENTORS EDWARD F.. MYERS x BY PAUL WINSOR 111 0 \o'oo zo'oo 30'00 40'00 6 t (LIFETIME OF TUBE)HRS. 04M

ATTORNEY United Sees iPaemQ" This invention relatesto pulse forming'circuits in general, but more particularly, to pulselgeneratin'gcircuits current pulses. r c

In conventional circuits utilizing power tubes, transistors, and the like, it is often times desirable to obtain not only'constant current pulses, but'consta'nt current pulses of variable widths. Moreover, a power tubeutilized in a pulse generating circuit is subject to deterioration'due to age so that whereas a new tube might conduct '160 thatare adapted to, provide substantially -s qu are' 'wave milliamperes for zero bias ,on its control grid, the same tube may, after a certain number of hours of tube operation, conduct only 100 milliamperes for zero bias on the control grid. Such change in tube characteristics must be monitored to assure that the pulse, generating circuit employing such power tube iscapable of maintaining the desired constant current output."

; circuit'of thepower tube of Fig. 1;

Fig. 3is a plot of curentoutput v. tube life of a ty'p, a1

2,925,492 PaitentedFeb; 16,

ICC

. 2 power tube generating the pulse whose widths and amplitudes are to be controlled.

It is yet another object toprovide a'simplifie'd system of pulse width control substantially independent. of-the triggering pulse that fires. the tube and without afiecting the rise time of the co'nstant amplitude current pulse produced by the generator. Q g

Various other advantages and objectscf theinvention will become apparent to those skilled in the art from the following description taken together with theaccompany ing drawing wherein:

Figylis an electric schematic of an embodiment-inf the invention; 7 V v,

Fig. 2 is an electric schematic of another embodiment of the invention wherein operation of the invention: is carried out without a transformer inv the'plateandg d pento'de utilized in thisinvention; and I v Fig. .4 is a voltage-time plot of a pulse generated by this invention inorder to enhance [the explanationpf how pulses arew idenedvby theinstant invention. f

Referring to Fig. l, there is shown a pentode l having a plate or anode 4, a suppressor grid'6 attached to grounded cathode 8 so, as td maintain the ,js ppfe'ssor. 'gridf-at substantially the same potential as the cathode} a, scr gridjltl', and acontrol grid 12'. .Atjransformer/T the plate-control grid circuit of ,pe'ntode tube,2- andjm- .cludes a' primary winding 14 in a circuit. that'incli ides only attaining constant current pulses of variable widths, I

but also of automaticallymaintaining constant current' output from the power tube used in the generator circuit, 2

regardless ofchange in tube characteristics-due to aging of the tube. The latter role of stabilizingcurrentoutput despite changeof tube life is accomplishedby utilizing .a novel. degenerative feedback circuit to the control .grid circuit of the power tube-ina manner hereinafter'to be described. The former role of achieving constant current pulses of variable widthsis carried out, in one embodiment ofthe invention, by biasing the control grid of the power tube through a series,circuit comprising a secondary of a transformer and a diode such' that thepower tube is biased to cut-off. --When itisdesired to trigger the power tube into conduction, a signal pulse is transmitted through the primary of the transformer so as to induce a potential in the secondary of the transformer of such a polarity as to overcome the cut-oifbias being appliedto the power tube and start the tube conducting. The tube conducts, yielding in its output circuit a sub-' stantially constant; amplitude pulse, such pulse normally I terminating when the signal pulse that has been applied to the a transformer primary terminates. However, as

soon as the powertube is about to cease conducting be-' cause of the return of the control grid to its cut-off bias,- a;- current path is made to take place through "thediode ,andsecondary of the transformer,-such current path being such as to maintain the control grid at a potential 7 that will enable the power tube to continue conducting m t mea e h te m n n o h t i er. p e-w th tgenerated. How-muchlo'ngergthetube will remainconductiv.e.will depend upon the circuit; parametersiof the transformer secondary.

improved pulse. generator.

-It is a further objecttol provide auitdmatic control of c ulse= amplitudes and pulse widths during the life ofa a consequent increase in-pulse Iwidth of-the output'pulse reference being made to Fig. 1 of the, drawing; Power series. circnit'that includes the aforementioned. diode'and I i f "Accordingly it is an object ofithis 'irivention'to provideplate: '4 and a secondary windingltii in a circuit that 'in- The present invention-carries ioutthe dnal. role oflnot secondary winding ltiisadiode ISha ingits anode joined 1;. v

to the control grid 12 and its cathode joined to aterininal of secondary winding 16. "A resistor 20and diode 22am provided to damp out any undesired oscillations that may arise inthe circuit that includes the secondary winding 16. 1 v Another transformer T comprises a primary winding 24 and a secondary winding .26, such secondary winding 26 having one of its terminals connected to the. secondary winding 16 of transformer T and its other terminal connected to a source of negative potential-e; so that control grid 12 is biased to cut-ofi through winding 26, winding, 16, and diode 18. v t,

A circuit path that is parallel to the current, pathbetween plate 4 and cathode 8 of tube 2 includesa variable positive terminal of a power supply, not shown, to the anode 4 through primary winding 14, supplying .a positive potential +V to the lead 38 of the resistor 36." Point P represents the 'junctionof the .cathode of diode 30, the lowpotential terminal of resistdf-BZ, the anode of diode 40, and one plate of capacitor .42. A positive potential +V is applied to the cathode of diode ill-to clampthe point P at the +V potential. i.

Theoperation of the variable width constantcurrent pulse'ge'nerator will now'be described withparticular tube, i2',;in' its quiescent state, hasa negative bias V' applied to its .grid, 12 through winding 26, winding 16,

and'diode 18. Such negative bias V is fchosen 'rn accordance with the operating characteristics oftube 2, tdv

supply. cut-off bias to the tube 2. A potential of -,-|,-V volts is appliedto various elements of. the tubej2 as shown, so that while the tube 2 is Cutoff, steady state current will flow from the +V terminal of the available power supply, most of such steady state current finding a path through variable resistor 28, diode 13, and to the negative terminal of the ..-V source of potential, since the positive +V bias on the cathode of diode 3!) disables diode 30 and prevents current flow from variable resistor 28 through diode 30. Another quiescent current path can be traced from the +V side of a source of power, through resistor 32, diode 40, to the +V terminal of a source of biasing voltage so as to maintain point P at a fixed clamping voltage.

When it is desired to trigger tube 2 into conduction, a pulse 46 of suitable amplitude and polarity is applied to input terminal 48 of primary winding 24 of transformer T The dot notation at the terminals of each winding indicates diagrammatically that when current enters a first Winding at its dotted terminal, a positive potential is induced at the dotted terminal of the winding that is transformer-coupled to said first winding. Consequently the current pulse 46 will induce a potential in winding 26 such that-the dotted terminal of winding 26 assumcs a positive potential that exceeds the negative bias -V such positive potential effectively disconnecting diode 18 and driving tube 2 into conduction. As tube 2 begins to draw current from its power supply so that the current enters primary winding 14 of transformer T there is transformer coupling between primary winding 14 and secondary winding 16 such that the dotted terminal of winding 16 assumes a positive potential while current is building up in tube 2. Such induced positive potential isfed back to the grid 12 so as to maintain tube 2 in its conducting state. -It is noted that the static current that was flowing through resistor 28, diode l8, winding 16, and winding 26, whenthe negative bias V was effectively applied to control grid 12 now flows through diode 30, capacitor 42, primary winding 14, load '44, tube 2 and to ground when diode 18 becomes discon nected due to a positive potential, in excess of the V pc' tential, appearing at the dotted terminal of winding 16. Such diversion of the static current from transformer winding 16 through the capacitor circuit lasts only so long as the diode 18 is cut oil, or as long as the pulse flowing through tube 2. The positive voltage induced at the dotted terminal of winding 16, and shown as dotted curve Y of Fig. 4, will build up in direct proportion to the rate of change of plate current flowing through the Wind- 'ing 14. As the plate current reaches saturation, the field of the plate winding 14 is no longer increasing and, therefore, the voltage induced in the winding 16 falls oif rapidly and is depicted by the substantially sharp drop of the dashed line Y of Fig. 4. As the potential appeanng at the dotted terminal of winding 16 falls, the diode 18 will commence conducting and there will be current flow from the +V source across the resistor 28, through the diode 18, through the winding 16, and windmg 26 to the V potential source. To this instantly applied D.-C. potential, the inductance 16 represents an impedance andthe voltage appearing across the inductance 16 is equal to L di/dt. Assuming that the inductance 16 has a fixed L value, it becomes clear that the voltage appearing thereacross is proportional to di/a't'. Depending on the setting of the variable resistance 28, the change of current flowing through the inductance 16 can be made greater or smaller. So long as the rate of change of current remains substantially constant, the potential appearing at the dotted terminal of 16 will be sufficiently posit ve to cause the tube 2 to remain in the state of conduction. When the rate of change of current (di/a't) reaches a small enough value so. that thedeveloped potential drop when measured from the .V reference is below the cutoff value of the tube 2, the tube will no longer conduct. As a generality this time is reached when there is a steady state current passing hrough. th ndu anc At wart me, hen s ead state current is reached, there is no lono'ger any positive potential appearing at the dotted terminal of winding 16 so that the cut-01f potential -.'V is reapplied to the control grid 12, and the generated pulse terminates.

Fig. 4 represents the waveform of the pulse generated by this invention. The waveform W is the general configuration of the pulse produced at the control grid 12 of tube 2. Dotted waveform Y represents the build up of positive potential at the dotted terminal of secondary winding 16. Initially the tube 2 is biased to cut-off by the application of a V bias to its control grid 12. Such V voltage is chosen, for purposes of illustration, as 20 volts. The triggering pulse 46 and the action of the regenerative coupling of windings 14 and 16 raise the potential of, control grid 12 towards zero potential. However clamping diode 30 prevents the grid 12 potential from rising above a certain predetermined potential, namely, near ground, andthe tube 2 conducts at a constant amplitude H. The amplitude of waveform W would normally drop to 20 volts at point Z upon cessation of the regenerative coupling of windings 14 and 16. However, as was explained hereinabove, a substantially constant rate of change of current di/dl takes place through diode 18 and winding 16 as soon as the potential at the dotted terminal of winding 16 goes below point P. Since the inductance L of winding 16 is constant, a substantially constant voltage The current available for flow through winding 16 is limited by the value of the resistance chosen for resistor 28. Z and Z represent different widths of generated pulses for different settings of variable resistor 28.,

Fig. 2 is similar to Fig. 1 save that the winding 14 and transformer coupling associated with T are removed. However, in removing the advantages of the regenerative effects provided by the blocking oscillator operation attained in Fig. 1, it is necessary to apply a wider triggering pulse 46' at the input terminal 48 than was applied at the terminal 48 of Fig. 1 in order to maintain tube 2 conductive for the required number of microseconds. .The operation of the pulse widening circuit comprising variable resistor 28, diode 18, winding 16, its parallel damping circuit of resistor 20 and diode 22, and secondary winding 26 still remains the same, namely, that of maintaining control grid 12 above cut-01f potential so that tube 2 conducts even after the triggering pulse 46 has terminated.

Load 44, shown in dotted block form, represents any suitable load to be driven by the generated pulse. The

, pulses generated by the instant invention have particular instant application.

utility in driving an array of magnetic cores, wherein such cores are of the type that have substantially square hysteresis loop characteristics. The cores are bistable elements that present relatively large loading when each is in the other stable state. For proper switching of such cores it is necessary to apply constant current pulses to switching windings associated with the cores so that the variable load presented by such cores can be driven without diminution of power to anyof the cores in the array. A constant current driver, of which the instant invention is an improvement, has been filed by John Paul I ones on May 24, 1954, and was given the Serial No. 431,678. The-Jones application is assigned to the assignee ofthe The' amplitude control of the generated pulse is obtained by the network that includes resistor 36, capacitor 42,resis tor 32 and diodes 30 and 40. It will be assumed t at he ube selec e n h 'nn pulse enera-torn.

liamperes v.-tube lifein hours. In the instant case, it'

is desired to control the amplitude of the generated variable width pulse between'a range of 100-110 ma, for

zero volts bias on the control grid 12. A-positive reference voltage +V is placedat the cathode of diode 40 so that point P is maintained at this '+V potential. When the tube 2 is new, the resistor 36i's chosen'so that the amount of voltage drop for-100 matcurrent flowing through .the tube 2 will be substantially that of the potential +V1'but opposite'in polarity: When'current through a 'tube 2 exceeds 100 mag-the potential at P becomes in K creasingly negative due 'to the increased potential' drop across resistor 36. Such increased potential drop can, by proper selection of resistor 36, be suflicient to overcome the +V potential being applied to diode 30 through diode 40 and render the cathode ofdiode 30 negative. Diode 30 now conducts so that the static current" which flowed through resistor 28 and diode18 will now flow through resistor '28, diode 30, capacitor 42 and through tube 2 to ground. Such current pulse lowers the potential of point Pas well'as con t r ol grid 12 so'that plate current diminishes. The automatic amplitude: control is maintained throughout the life of the tube; and 'the stability and range of such control depends on the initial selection of the value of resistor 36 and the originalsetting of the potential +V The current'ou'tput of the power tube 2 will be between 100-410 ma. as shown in Fig. 3.

A typical, though nowiselimiting set of values, for

' a ,6197 or 6LC6 tube is: r

The aforedescribed invention is capable of attaining variable width and constant amplitude pulses without reliance upon active elements such as tubes. Since the passive elements comprising the instant invention can be manufactured to retain their electrical characteristics for a relatively long time for the range in which the current driver will operate, thepresent circuit is rugged, reliable, and economical.

What is claimed is:

1. A variable-width current driver comprising: an amplifier tube having input and output electrodes; a variable resistance; an inductance; means connecting the lower end of said resistance to the upper end of said inductance, thereby to connect said resistance and inductance in series forming an RL voltage divider circuit; a direct-current potential source connected across said series-connected resistance and'inductance with the highpotential side of said source connected to the upper end of said resistance; said resistor and inductance respectively having characteristic values to render the steady-state potential at the lower end of said resistance relatively negative; means for connecting said lower end of said resistance to an input electrode of said tube to apply said relatively negative potential thereto to bias said tube beyond cutoff; transformer-means having primary to said inductance, said primary winding coupledto receive an input current pulse to produce in response thereto a voltage at said upper end of; said inductance of 1 thereby to drive said tube into conduction for a period of time equal to the period during .which the flux resulting from said input current pulse is changing at a rate sufliciently fast to produce a voltage of overriding and secondary windings, said secondarywinding coupled putcircuit of said tube for deriving an outputr'pulse" whose duration is a function of the period of conduction of said tube as controlled by the'setting of said variable resistance;

2. Apparatus as claimed in claim 1 characterized in that said means connecting the lower end-of said resistance and the upper end of said inductance includes a diode poled to be reversed biased by the overriding voltage produced at the upper end of said inductance 'by said input current'pulse, thereby to disconnect said inductance from said resistance. 1 3. Apparatus as claimed in claim Z-"further characterized in that asecond resistance is connectedbetween the lower end of said ;var iable resistancefand the potential terminal of said direct-current soui ce in parallel with said variable resistance, andfur'ther "characterized in that'diode clamping means are provided for preventing t v V said input electrode of'said tubeufrom rising abov a preselected value of potential.

4. Apparatus as claimed in claim that an inductance is included in the ouput circuit of said tube regeneratively coupled to said first-mentioned inperiod beyond the termination of said input pulse. 7

5. A variable width current pulse generating circuit comprising an electron transmitting device having an input element, an output element and at least a firstcontrol element, a' variable impcdance means having first and second end terminals, an inductance meanshaving first and second end terminals with said first end terminal connected to said impedance means second end terminal a polarity and of a magnitude to override said bias,

to form a variable voltage divider circuit, a direct current potential source having a high potential output and a low potential output, first circuitry means connecting V saidimpedance means first end terminal to said direct current potential source high potential output, second circuity means connecting said direct-current potential source low potential output to said inductance means second end terminal, said impedance means and said inductance means having characteristic values which provide at the second end'terminal .of said impedance means a potential whose value is relatively negative, third circuitry means connecting said impedance means a second end terminal to said control element to apply said relatively negative potential thereto to bias said electrontransmitting device into a state of non-conduction, a

' source of positive input signals coupled to said inductance means second end terminal to be applied thereto thereby biasing said electron transmitting device to conduct,

said electron transmitting device remaining in a state of conduction for an initial period of time'equal to the time period of a positive input signal applied and in addition for a continuing period of'time after said input signal terminates whichis as long as the potential, developed by the changingcurrent flowing through said in-' ductance in response to said direct current potential applied and appearing-at said inductance first end terminal, biases said electron transmitting device for conduction, and 'output means coupled'to said electrontranse put element, an output element, and at least a first control 51 r element, a variable impedance means having first and second end terminals, ,a first inductance means having first and second end terminals with said first end terminal 1 characterized in 7 animated esa dimpsean'ee moan cond end t rminal tie erm a vari ble voltage di der-cir i a d rec c r n mtenti'al. e rce ha in high po outpu nd a 10w pote tial utpu first c cu y an connecting a d impedance means first end terminal to said direct current potential source high potential output, transformer means having primary and secondary windings, said secondary winding coupled between said first inductance second end terminal and said direct current potential source low potential output, said impedance means and said first inductance means having characteristic values which provide at the second end terminal of said impedance means a potential whose value is relatively negative, second circuitry means connecting said impedance means second end terminal to said control element to apply said relatively negative potential thereto to bias said electron transmitting device into a state of non-conduction, a source of positive input signals, said primary winding coupled to said source to receive input signals and thereby produce in response'a relatively positive voltage at said first inductance means first end terminal, said relatively positive voltage being sufficiently positive to bias said control elernentto cause said electron transmitting device to conduct, a-second inductance means connected to the output element of said discharge device and inductively e a ed. a ai first inductan e mane said elect-reels ha e de c rema ning n. a sta e Qt sQniu ion. e ial pe i d f; time qual a timeper pd are pqs ivs npu nal i dtmed.w 0 .1, aid. se d ry nd n vfo a c nt nu us s c n P r Qt t me so l n as s d as en inductance means induces a positive potential on said first inductance means and for a continuous third period of time after said input signal terminates which is as long as the potential, developed by the changing current flowing in response to said direct current potential source through said first inductance and appearing at said firstinductance first end terminal, biases said electron transmitting device for conduction, and output means coupled to said electron transmitting device output element to provide an output signal in accordance with said electron transmitting device conduction period.

References Cited in the file of this patent UNITED STATES PATENTS Great Britain V Sept. 8, 195,4 

